Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-08-08
2003-01-14
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S048000, C525S064000, C525S258000, C525S263000, C525S301000
Reexamination Certificate
active
06506847
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method for controlling the molecular weight of polyolefin graft copolymers.
BACKGROUND OF THE INVENTION
Polymer molecular weight and its distribution are critical parameters affecting the final properties of a graft copolymer. During free radical polymerization, the molecular weight of the polymer is mainly determined by the reaction temperature, the concentration of free radical initiators, and the monomer concentration.
In a gas mixed reactor, a lower polymerization temperature will usually reduce the gas phase fouling due to a lower monomer vapor pressure in the gas phase. The main issue associated with a lower reaction temperature is that graft copolymers prepared in this manner have an undesirably high molecular weight. Although increasing the initiator concentration will help to reduce the molecular weight, the molecular weight dependence on the initiator concentration is less pronounced due to the very low initiation efficiency observed for graft polymerization. In addition, graft copolymerization is carried out using a pure monomer feed and therefore the monomer concentration is not an adjustable parameter for polymer molecular weight control.
Using a chain transfer agent in free radical polymerization can reduce the polymer molecular weight by its chain-breaking action. This results in a decrease in the size of the propagating polymer chain. The effect of chain transfer on the polymerization rate is dependent on whether the rate of re-initiation is comparable to that of the original propagating radical. Organic compounds such as mercaptans or alkyl bromides have been widely used in polymerization processes to control polymer molecular weight. For example, U.S. Pat. No. 4,000,220 discloses the use of chain transfer agents such as mercaptans, thiopropionic acid, carbon tetrachloride, and dimeric alpha-methylstyrene in the production of thermoplastic graft copolymer resins. U.S. Pat. No. 4,001,349 discloses the use of chain transfer agents such as mercaptans for the preparation of grafted products of styrene and saturated polyolefinic elastomers. U.S. Pat. No. 4,308,354 discloses the manufacture of transparent, impact-resistant polymers from polybutadiene rubber and a mixture of methyl methacrylate, styrene, and methyl or ethyl acrylate by polymerizing in the presence of an initiator and a chain transfer agent such as an alkyl mercaptan. U.S. Pat. No. 4,427,826 discloses polymerizing 1,3-diene rubber and one or more vinyl monomers, with or without a solvent, in the absence of a free radical initiator and in the presence of a mercaptan chain transfer agent. The chain transfer agent often produces an undesirable odor or color in the final product. Removing chain transfer agent residue in the polymer could also be a difficult task.
There is therefore a need for a chain transfer agent that can effectively reduce polymer molecular weight without leaving an undesirable residue in the final product.
SUMMARY OF THE INVENTION
The process of this invention for reducing the molecular weight of graft copolymers comprises, in a substantially non-oxidizing atmosphere,
(1) treating a propylene polymer material with an organic compound that is a free radical polymerization initiator,
(2) treating the propylene polymer material over a period of time that coincides with or follows (1) with or without overlap, with about 2 to about 240 parts per hundred parts of the propylene polymer material, of at least one vinyl-substituted grafting monomer capable of being polymerized by free radicals, in the presence of about 0.5% to about 5%, based on the total weight of monomer, of a polymerizable chain transfer agent that is a derivative of allyl alcohol, and
(3) removing any unreacted monomer from the resulting grafted propylene polymer material, decomposing any unreacted initiator, and deactivating any residual free radicals in the material.
Carrying out the graft polymerization reaction in the presence of an allyl alcohol derivative that is polymerizable by a free radical initiator effectively reduces the molecular weight of the graft copolymer. The concentration of chain transfer residue in the final product is low because the chain transfer agent is incorporated into the polymer chain.
DETAILED DESCRIPTION OF THE INVENTION
“Substantially non-oxidizing environment” is the environment or atmosphere to which the olefin polymer material is exposed during the preparation of the graft copolymer and means an environment in which the active oxygen concentration, i.e., the concentration of oxygen in a form that will react with the free radicals in the polymer material, is less than 15%, preferably less than 5%, and most preferably less than 1% by volume. The most preferred concentration of active oxygen is 0.004% or lower by volume. Within these limits, the non-oxidizing atmosphere can be any gas, or mixture of gases, that is oxidatively inert toward the free radicals in the propylene polymer material, e.g., nitrogen, argon, helium, and carbon dioxide.
The propylene polymer material that is used as the backbone of the graft copolymer can be:
(a) a crystalline homopolymer of propylene having an isotactic index greater than 80, preferably about 85 to about 99;
(b) a crystalline copolymer of propylene and an olefin selected from the group consisting of ethylene and 4-10 C alpha-olefins, provided that when the olefin is ethylene, the maximum polymerized ethylene content is 10% by weight, preferably about 4%, and when the olefin is a 4-10 C alpha-olefin, the maximum polymerized content thereof is 20%, preferably about 16%, by weight, the copolymer having an isotactic index greater than 85;
(c) a crystalline terpolymer of propylene and two olefins selected from the group consisting of ethylene and 4-8 C alpha-olefins, provided that the maximum polymerized 4-8 C alpha-olefin content is 20% by weight, preferably about 16%, and, when ethylene is one of the olefins, the maximum polymerized ethylene content is 5% by weight, preferably about 4%, the terpolymer having an isotactic index greater than 85;
(d) an olefin polymer composition comprising:
(i) about 10% to about 60% by weight, preferably about 15% to about 55%, of a crystalline propylene homopolymer having an isotactic index greater than 80, preferably about 85 to about 98, or a crystalline copolymer of monomers selected from the group consisting of (a) propylene and ethylene, (b) propylene, ethylene and a 4-8 C alpha-olefin, and (c) propylene and a 4-8 C alpha-olefin, the copolymer having a polymerized propylene content of more than 85% by weight, preferably about 90% to about 99%, and an isotactic index greater than 85;
(ii) about 5% to about 25%, preferably about 5% to about 20%, of a copolymer of ethylene and propylene or a 4-8 C alpha-olefin that is insoluble in xylene at ambient temperature, and
(iii) about 30% to about 70%, preferably about 20% to about 65%, of an elastomeric copolymer of monomers selected from the group consisting of (a) ethylene and propylene, (b) ethylene, propylene, and a 4-8 C alpha-olefin, and (c) ethylene and a 4-8 C alpha-olefin, the copolymer optionally containing about 0.5% to about 10% of a diene, and containing less than 70% by weight, preferably about 10% to about 60%, most preferably about 12% to about 55%, of polymerized ethylene and being soluble in xylene at ambient temperature, and having an intrinsic viscosity of about 1.5 to about 4.0 dl/g,
wherein the total amount of (ii) and (iii), based on the total olefin polymer composition, is about 50% to about 90%, the weight ratio of (ii)/(iii) is less than 0.4, preferably 0.1 to 0.3, and the composition is prepared by polymerization in at least two stages, and has a flexural modulus of less than 150 MPa; or
(e) a thermoplastic olefin comprising:
(i) about 10% to about 60%, preferably about 20% to about 50%, of a crystalline propylene homopolymer having an isotactic index greater than 80, or a crystalline copolymer of monomers selected from the group consisting of (a) ethylene and propylene, (b) ethylene, propylene, and
Asinovsky Olga
Basell Poliolefine Italia S.p.A.
Seidleck James J.
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